1. Field of the Invention
This invention relates to a semiconductor laser. This invention particularly relates to a semiconductor laser, which comprises a Group III-V compound semiconductor and produces a laser beam having a wavelength in the band of 0.63 .mu.m to 1.1 .mu.m.
2. Description of the Prior Art
As a semiconductor laser, which produces a laser beam having a wavelength in the band of 0.7 .mu.m to 0.85 .mu.m, there has heretofore been known the semiconductor laser comprising an n-GaAs substrate, an n-AlGaAs cladding layer, an n- or i-AlGaAs optical waveguide layer, an i-AlGaAs active layer, a p- or i-AlGaAs optical waveguide layer, a p-AlGaAs cladding layer, and a p-GaAs capping layer, which layers are formed on the substrate. Such a semiconductor laser is described in, for example, a literature (1): "IEEE Journal of Quantum Electronics," QE-20, 1984, pp. 1119-1132, by W. T. Tsang.
Also, as a semiconductor laser, which produces a laser beam having a wavelength falling in the aforesaid band, there has heretofore been known the semiconductor laser comprising an n-GaAs substrate, an n-InGaP cladding layer, an n- or i-In.sub.x2 Ga.sub.1-x2 As.sub.1-y2 P.sub.y2 optical waveguide layer, an i-In.sub.x1 Ga.sub.1-x1 As.sub.1-y1 P.sub.y1 active layer (wherein x1&lt;x2, y1&lt;y2), a p- or i-In.sub.x2 Ga.sub.1-x2 As.sub.1-y2 P.sub.y2 optical waveguide layer, a p-InGaP cladding layer, and a p-GaAs capping layer, which layers are formed on the substrate. Such a semiconductor laser is described in, for example, a literature (2): "Japanese Journal of Applied Physics," Vol. 31, 1992, pp. L1686-L1688, by J. S. Yoo, et al.
Further, as a semiconductor laser, which produces a laser beam having a wavelength in the band of 0.63 .mu.m to 0.73 .mu.m, there has heretofore been known the semiconductor laser comprising a GaAs substrate, an n-InGaAlP cladding layer, an i-InGaAlP optical waveguide layer, an InGaP tensile strained quantum well, an i-InGaAlP optical waveguide layer, a p-InGaAlP cladding layer, a p-InGaP barrier reducing layer, and a p-GaAs capping layer, which layers are formed on the substrate. Such a semiconductor laser is described in, for example, a literature (3): "IEEE Journal of Quantum Electronics," QE-30, 1994, p. 593, by D. P. Bour, et al.
Furthermore, as a semiconductor laser, which produces a laser beam having a wavelength of 1.03 .mu.m, there has heretofore been known the semiconductor laser comprising a GaAs substrate, an n-InGaP cladding layer, an i-InGaAsP optical waveguide layer, an InGaAs compression strained quantum well, an i-InGaAsP optical waveguide layer, a p-InGaP cladding layer, and a p-GaAs capping layer, which layers are formed on the substrate. Such a semiconductor laser is described in, for example, a literature (4): "IEEE Photonics Technology Letters," Vol. 6, 1994, pp. 1-3, by G. Zhang, et al.
However, the structure described in the literature (1) has the drawbacks in that Al contained in the active layer is chemically active and apt to be oxidized, and therefore the end face of a resonator is readily deteriorated due to cleavage. Accordingly, the reliability of the semiconductor laser cannot be kept high.
The structure described in the literature (2) copes with the aforesaid drawbacks. However, this structure has the drawbacks in that the growth of the InGaP material markedly depends upon the orientation of the substrate surface and the growth conditions, and therefore a crystal having good quality cannot always be obtained with good reproducibility. These drawbacks are pointed out in, for example, a literature (5): "IEEE Journal of Quantum Electronics," QE-27, 1991, p. 1483, by H. Hamada, et al.
Further, as is pointed out in the literature (5), the structures described in the literatures (3) and (4) have the drawbacks such that, for example, the growth of the InGaAlP type of material markedly depends upon the orientation of the substrate surface and the growth conditions, and therefore a crystal having good quality cannot always be obtained with good reproducibility.